Specifically designed molecular probes will be used to obtain detailed information regarding the mechanism of the liver microsomal cytochrome P-450-mediated oxidation of organic compounds. Deuterium-labeling techniques and monitoring of molecular rearrangements, which have been developed over several years with a model system, will be applied to the enzyme to determine the role and nature of carbon-free radicals that appear to be generated in the course of the catalytic cycle. The fate of these radicals may be intimately involved with the known hepatotoxicity of a large number of compounds. The results of the study may help to elucidate the mechanistic details by which xenobiotic chemical contaminants become activated toward carcinogenesis.